The present invention relates to an alarm device for signalling a reduction of the pneumatic pressure of vehicle tires with the aid of a resonance phenomenon of electro-magnetic coupling.
As alarm devices for sensing abnormal change of an internal pneumatic pressure of vehicle tires when running and for informing it to a driver, mention may be made of a signal transmission system and a resonance phenomenon of electromagnetic coupling.
An alarm device with the aid of a signal transmission system, in case of adopting it as, for example, unattended operation of a new traffic system or an automatic train stop device, requires a transmitter and a receiver for every one of a plurality of rolling stocks or vehicles for constructing one train, so that its construction becomes complicated and expensive, while it is necessary to prevent interference between transmitters and receivers of each vehicle.
An alarm device with the aid of a resonance phenomenon of electromagnetic coupling, as apparent from Japanese Patent Application Ser. No. 150,235/76 and Japanese Patent Application Ser. No. 150,236/76, solves a problem of the signal transmission system, but a light emitting diode or a lamp is energized or lighted when stopping even if an internal pneumatic pressure is normal and then an alarm is undesirably generated. Conversely speaking, it means automatic inspection whether the circuit of the alarm device is normally operated.
However, even if the pneumatic pressure of a tire is normal as described above and if an alarm is generated when stopping, when a means for appealing the sense of hearing such as a buzzer or the like is employed as an alarm device, the alarm buzzer is annoyingly rung at every stopping and such buzzer cannot be used for unattended operation of a new traffic system or automatic train stop device or the like.